Chelicerates

What are Chelicerates? Chelicerates are named for the pair of feeding appendages in front of the mouth, called chelicerae. Members of this group lack antennae and have a body divided into two distinct portions: prosoma (head region) and opisthosoma (main body). Spiders, ticks, scorpions, and horseshoe crabs are familiar chelicerates. Less familiar chelicerates include the sea spiders (pycnogonids) and the extinct relatives of horseshoe crabs called sea scorpions (eurypterids). Eurypterids first appear in the Ordovician and were extinct by the Permian, while most of the chelicerates began to appear in the Devonian and are still around today.

First known fossil occurrence: Ordovician.

Last known fossil occurrence: Quaternary. This group has living relatives.